The first-half of the 70th Week of Daniel is 1,260 days, and the
second-half is 1,290 days totaling 2,550 days in length. If the
70th Week were to begin with the 'covenant with many' on Rosh
Hashanah Sept. 24, 2014 during the lunar tetrad of 2014-15 it
would conclude 2,550 days later on Day of Atonement/Yom Kippur
Sept. 16, 2021.
I believe that the '70th Week of Daniel' will begin on 'Feast of
Trumpets' and conclude seven years (2,550 days) later on the
'Day of Atonement'.